On Tue, Oct 12, 2021 at 12:17:42PM -0600, Jens Axboe wrote:
> Trivial to do now, just need our own io_batch on the stack and pass that
> in to the usual command completion handling.
>
> I pondered making this dependent on how many entries we had to process,
> but even for a single entry there's no discernable difference in
> performance or latency. Running a sync workload over io_uring:
>
> t/io_uring -b512 -d1 -s1 -c1 -p0 -F1 -B1 -n2 /dev/nvme1n1 /dev/nvme2n1
>
> yields the below performance before the patch:
>
> IOPS=254820, BW=124MiB/s, IOS/call=1/1, inflight=(1 1)
> IOPS=251174, BW=122MiB/s, IOS/call=1/1, inflight=(1 1)
> IOPS=250806, BW=122MiB/s, IOS/call=1/1, inflight=(1 1)
>
> and the following after:
>
> IOPS=255972, BW=124MiB/s, IOS/call=1/1, inflight=(1 1)
> IOPS=251920, BW=123MiB/s, IOS/call=1/1, inflight=(1 1)
> IOPS=251794, BW=122MiB/s, IOS/call=1/1, inflight=(1 1)
>
> which definitely isn't slower, about the same if you factor in a bit of
> variance. For peak performance workloads, benchmarking shows a 2%
> improvement.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> drivers/nvme/host/pci.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 4713da708cd4..fb3de6f68eb1 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -1076,8 +1076,10 @@ static inline void nvme_update_cq_head(struct nvme_queue *nvmeq)
>
> static inline int nvme_process_cq(struct nvme_queue *nvmeq)
> {
> + struct io_batch ib;
> int found = 0;
>
> + ib.req_list = NULL;
Is this really more efficient than
struct io_batch ib = { };
?
